Smoke detectors are usable to monitor a region of interest. While they are usable individually, there has long been an interest in interconnecting a plurality of detectors using a common communication link. One such system has been disclosed and claimed in Tice et al. U.S. Pat. No. 4,916,432 entitled Smoke and fire Detection System Communication. The Tice et al. patent is assigned to the assignee hereof and incorporated herein by reference.
While systems of the type disclosed in the Tice patent are useful there are alternate circuit configurations for interconnecting detectors. One such alternate configuration has been disclosed in U.S. Pat. No. 4,207,558 entitled Interconnecting Circuit For A Plurality Of Alarm Units.
So-called four wire detectors can be configured to operate off of a common two wire power loops. Such loops can be used to supply energy to the detectors coupled thereto. Alternately, the loop can be used to transfer information as in the Tice et al. patent.
Other connections to such detectors can be used via a second loop, to provide status signals. Such detectors, if coupled to an HVAC-type duct, can be used to terminate the operation of one or more fans, or to close one or more dampers in the presence of an alarm condition.
In known installations, a single such detector will usually control a single fan, blower, damper or other control device. In known installations, where multiple fans, blowers or dampers were to be controlled, external control panels or relays have been used.
It would be desirable to be able to control multiple fans, blowers or the like without having to incorporate additional relays or control panels. It would also be desirable to be able to change the operational state of a plurality of such elements without necessarily causing all detectors to emit an alarm indicator.